The present invention relates generally to an improved device for shifting lenses in a barrel to accomplish zooming and macro-focusing operations, in addition to a focusing operation, and it relates more particularly to a lens shifting device having improved shock resistance.
Hitherto, in lens barrels of the subject type, the axially movable frame for a lens group positioned on the side closest to an object, that is, the frontmost position in the lens system, like other movable lens frames, is so constructed as to be moved relative to a fixed cylinder by means of follower of coupling of pins and cam grooves. For this reason, when a shock or an impact is imparted to the movable lens frame, then the pins and cam grooves are likely to be damaged. For improving the shock resistance of the lens barrel and to overcome the aforesaid shortcomings, it has been proposed to provide on the fixed cylinder a protective lens barrel constructed to shelter the movable lens frames in a manner that the front movable lens frame does not project from the end of the lens barrel, with the overall length of the lens barrel including the protective lens barrel being constant, wherever two or more movable lens frames are moved along the optical axis due to a focusing operation or a zooming operation. Thus, the protective lens barrel protects the front movable lens frame, even when it moves to its frontmost position along the optical axis of the lens system.
For the above purpose, the protective lens barrel is so dimensioned as to project a considerable length. As a result, in order to ensure a sufficient angle of view and quantity of incident light, particularly in the case where the front movable lens frame assumes its most retracted position within the lens barrel, at least the front portion of the lens barrel including the protective lens barrel member must have a substantially large interior diameter. For this reason, the lens barrel for a lens system of the subject type must be of large diameter, as well as of great length, thus leading to an increase in size and weight. This necessarily leads to an increase in the diameters of lens barrel accessories such as color filters, polarizing filter and the like, with an accompanying increase in the cost thereof, and a loss or lack of interchangeability of the accessories between the instant lens barrel and other lens barrels.